Over the last 10-15 years there has been much discussion in the agricultural realm about the utility of fungicide trials conducted on small plots, vs those on larger plots. Small plots typically are 5-10’wide, and 20-50’ long, depending on the crop and study. Large plots typically consist of strips of varieties or treatments, and therefore are as wide as the width of a sprayer or planter and typically span a cross section of the field. Today I’m going to discuss the advantages and disadvantages of both types of studies and go over some new research on the subject.
Small plot research can be conducted on a relatively small area, easily replicated, and allows for multiple treatments to be tested simultaneously (think nitrogen x spacing x fungicide timing for example). Limitations in plot size can result in larger than typical variability, especially with corn research. This is because a small amount of ear loss at harvest can have a fairly large effect on overall plot yield, and the number of plants in the plot is small. Thus, small differences in the absolute number of plants in the plot and ears harvested can result in more variability in yield from plot to plot. In the past, many also discounted small plot research due to perceived edge effects from and alleys influencing results. Edge effects result from the plants on the outside of plots experiencing a slightly different environment than those on the inside. In small plot research, the edge effect can be large in some instances. However, at least with fungicide work, research indicates that alleys and edge effects do not influence overall results (Vincelli and Lee 2015). Edge effects can be minimized by reducing the size of alleys, harvesting a central portion of the plot, and waiting until later in the growing season to cut alleys.
Contrast this with larger scale studies such as strip trials. These studies do not suffer from as many issues with yield-related variability, at least regarding corn, because plots are much larger and therefore grain samples are less influenced by ear loss and limited population. Edge effects are minimized due to large plot size. The downside is that due to the plot size, strip trials are often limited to a small number of treatments.
That brings me to my last point. Some people, for whatever reason, completely discount small plot research results. Often, many of the aforementioned claims are mentioned in this argument. In the end, is there really any difference in results? Researchers at Iowa State recently published a study that examined small plot and strip plot fungicide trials conducted in Iowa from 2008-2015 (Kandel et al 2015). A total of 230 strip plot trials and 49 small plot trials were included in the analysis. Based on their analysis, the researchers found that the yield responses for the various treatments were similar. However, the data from small plot trials were slightly more variable. For example, to detect a given yield response, a split plot trial would need three treatment replications per field and 12 locations, whereas a small plot trial would need seven replications at each site and 12 locations. Their results show that small plot data show the same results as the large plot data, but might need a little more replication to detect a difference when compared to strip trials. Both small plot and large plot data are useful for agriculture, and both have their advantages and disadvantages. However, neither should be discounted when it comes to providing useful information to growers.
Lastly, I will leave you with a link to a great little article from the University of Nebraska called “Field Studies: What do you mean 5 bushels per acre is not significant?” In this article the authors do a great job of discussing research and terms such as significance and variability. This is a good read heading into meeting season and Crop School. Find the article here
- Vincelli and C. Lee, 2015. Influence of open alleys in field trials assessing yield effects from fungicides in corn. Plant Disease pp 263-266.